Embedding a first digital information signal into a second digital information signal for transmission via a transmission medium

ABSTRACT

A transmitter is disclosed for transmitting a first and second digital information signal. Said first digital information signal comprises first frames having at least a first synchronization signal and a data portion stored in them. The transmitter processes the second digital information signal into subsequent second frames comprising blocks of information of the second digital information signal. Composite frames have been obtained by inserting a second synchronization signal and at least the data portion of the first frames into the second frames by using buried data techniques. Prior to inserting at least the data portion of the first frame into a second frame the first synchronization signal is stripped from the first frame. The sequence of composite frames is transmitted via the transmission medium.

The invention relates to a transmitter for transmitting a first andsecond digital information signal via a transmission medium, said firstdigital information signal comprising first frames having at least afirst synchronization signal and a data portion stored in them, thetransmitter comprising:

-   input means for receiving the first and second digital information    signal;-   processing means for processing the second digital information    signal into subsequent second frames, said second frames comprising    blocks of information of the second digital information signal;-   signal combination means for inserting a second synchronisation    signal and at least the data portion of a first frame into a second    frame of the second digital information signal so as to obtain a    composite frame;-   output means for supplying the composite frames to an output    terminal so as to obtain a composite signal to be transmitted.

The invention further relates to a receiver for receiving a compositesignal from a transmission medium and generating a first and a seconddigital information signal, to a record carrier obtained with thetransmitter, when in the form of an apparatus for recording informationon a record carrier, and to a transmission method.

Transmitters and receivers defined above are commonly known in the formof transmitters for transmitting an MPEG encode signal. Transmissionsystems usually use multiple layers. Synchronisation becomes possibleonly by the use of sync patterns in these layers. However, these syncpatterns in a system having multiple sync patterns reduces thetransmission efficiency. For example in DVD-Video sync patterns are usedin both the system stream layers as well as in the elementary streamlayers. Only the sync pattern in the highest system layer is used forsynchronisation on the system stream. The sync patterns in theelementary streams are used for synchronization during decoding of saidelementary stream. Further, DAB uses sync patterns in both the systemstream layer as well as in the elementary stream layer. However adecoder uses only one of both.

The invention aims at providing transmitters and receiver having an moreefficient method of transmitting and receiving a first and a seconddigital information signal, whereby said first digital informationsignal comprises first frames having at least a second synchronizationportion.

The transmitter in accordance with the invention is characterized inthat signal combination means are adapted to strip the firstsynchronization signal from said first frames prior to inserting atleast the data portion of the first frames into the second frames.

The receiver in accordance with the invention is characterized in thatthe receiver further comprises;

-   synchronization signal generator means for generating a first    synchronization signal;-   signal combination means for combining the first synchronization    signal and the at least the data portion of the first digital    information signal so as to obtain a first frame of the first    digital information signal;-   second output means for subsequently supplying the first frames of    the first digital information signal to a first output terminal so    as to obtain the first digital information signal.

The invention is based on the following recognition. In for example aburied data channel in a PCM signal any other information signal may bestored. To be able to retrieve the information signal from said burieddata channel the buried data channel comprises frames whereby each framehas a synchronization signal. After detecting said synchronizationsignal, a frame from the buried data channel can be retrieved from thePCM signal. If the information signal stored in the buried data channelis an encoded signal comprising a sequence of frames each having asynchronization signal, for example an MPEG encode signal, saidsynchronization signal has to be retrieved in a receiver to be able todecode said sequence of frames. However, if each frame in the burieddata channel comprises only one frame of the encoded signal, saidsynchronization signal in a frame of the encoded signal needs not to betransmitted, there said synchronization signal can be generated in thereceiver each time a frame in the buried data channel is retrieved. Thusin a transmitter, prior to inserting a frame of the encoded signal intothe buried data channel the synchronization signal is striped from saidframe. In a receiver the synchronization signal is generated andcombined with the data retreived from a frame of the buried data channelso as to obtain a frame of the encoded signal. By doing this the datacapacity needed to transmit an additional signal comprising a sequenceof frames is reduced. This reduction may be used to use less capacity inthe PCM signal for the buried data channel, resulting in a higherquality PCM signal. On the other hand, the extra data capacity in theburied data channel, obtained by removing the synchronization signal maybe used for transmitting a less compressed data signal being normally abetter representation of the data signal.

These and other objects of the invention will become apparent from andelucidated further with reference to the embodiments described in thefollowing figure description in which

FIG. 1 shows an embodiment of a transmitter in accordance to theinvention,

FIG. 2 shows an embodiment of a receiver in accordance to the invention,

FIG. 3 shows a Buried data frame-structure with header,

FIG. 4 shows the de-randomization circuit,

FIG. 5: shows The bits in the buried_data_frame need to be inserted intothe de-randomization circuit in a specific order,

FIG. 6 shows a CRC-check diagram,

FIG. 7 shows A frame of 1152 stereo PCM samples corresponds to 192 F3frames,

FIG. 8 shows a Buried data frame structure without header,

FIG. 9 shows the distribution of Encrypted MPEG2 audio data the burieddata channel and the physical channel.

FIG. 10 shows another specific embodiment of a transmitter in accordanceto the invention.

FIG. 1 shows an embodiment of a transmitter in accordance to theinvention. The transmitter has a first input terminal 4 for receiving afirst digital information signal. Said first digital information signalcomprises first frames. The first frames comprise at least a firstsynchronization signal and a data portion. The first digital informationsignal could be an MPEG encoded signal. The transmitter has a secondinput terminal 2 for receiving a second digital information signal. Thesecond digital information signal is for example a normal CDDA signal(Compact Disc Digital Audio). The second digital information is suppliedto a processing unit 6. The processing unit 6 divides the second digitalinformation signal into subsequent blocks of information. From thesubsequent blocks of information the processing unit 6 generatessubsequent second frames. In a preferred embodiment the second digitalinformation signal is a normal CDDA signal having PCM samples.Preferably, a second frame comprises 1152 PCM samples. Each frame isconsists of 3 PCM sub frames, each having 384 PCM samples. It should benoted that the number 9 PCM sub-frames, each having 128 PCM samples, issuitable as well.

The transmitter further comprises a sync generator unit 8 for generatinga second synchronization signal. The second synchronization signal issupplied to a signal combination unit 10. The combination unit 10 makespreferably use of buried date techniques to determine a buried datachannel in the PCM samples of a second frame. By using buried datatechniques the perceived SIN ratio of the transmitted PCM signal, whichcomprises a buried data channel in the least significant bits of the PCMsamples, is approximately the same as the SIN ratio of the original PCMsignal. The combination unit 10 inserts the second synchronizationsignal in the buried data channel. Preferably, the synchronizationsignal is inserted in the second frame such that the frame starts with async pattern in the two least significant bits of its first 6 L+R PCMsamples. The data to be stored in the buried data channel is preferablyinserted in the PCM L and R channel on a sample by sample interleavingbasis. FIG. 3 shows an embodiment of a second frame. Each second framestarts with header information. The header information of each framecomprises the synchronization signal, the bit allocation of the 3sub-frames defining the PCM bits belonging to the buried data channel.Furthermore, the buried data frame payload is an example of the leastsignificant bits LSB of the L+R PCM samples, which are determined byburied data techniques to be used to carry data bits of the buried datachannel. FIG. 5 shows an example how the bits in the buried data framecould inserted. Firstly, the header is alternately stored in the LSB'sof the first 4 Left and Right PCM samples of the first sub-frame. Next,the data bits are alternately inserted in the allocated buried datapayload. In FIG. 5 the 3 LSB's of the PCM samples of the Left channeland the 2 LSB's of the Right channel are allocated to store data. Thenumber in the squares indicates the sequence in which the bits arestored in the buried data payload.

The signal combination unit 10 is arranged to insert at least the dataof a first frame into the buried data frame payload. Firstly, the firstsynchronization signal is stripped from the first frame by unit 12.Further, prior to writing the data portion of the first frames in theburied data frame payload the data portion of the first frame israndomized. By randomizing a burst of errors in the buried data framepayload will not result immediately to uncorrectable errors in the dataof the buried data channel. At last, the signal combination unit 10 isarranged to store in the last 16 bits of the buried data frame payload aCRC-16 word for error detection purposes. Therefore, the data bitsinserted in the buried data channel are fed through a LFSR (LinearFeedback Shift Register) with for example polynomial 0×8005. The finalstate of the LFSR is stored in the buried data CRC-16 word. The thusobtained composite frame is supplied to an output terminal. In the eventthat there is no capacity in the PCM samples for a buried data channel,only the header information is inserted in a second frame.

The functioning of the transmitter is as follows. The PCM frame consistsof 3 subframes each having 384 PCM samples. The 1152 PCM samples in aPCM frame represents a time length which matches exactly the MPEG-2Audio Layer II frame length. In IEC-61937 formatting the first 16 bitsof an MPEG Audio frame are unique for the CD Surround application(0×FFFC, 12 bit sync+ID=mpeg-1+Layer-II+protection=used). As the timelength of a PCM frame is equal to the time length of an MPEG frame, thefirst 16 bits of an MPEG frame need not transmitted. In a receiver said16 bits have to be placed before the extracted and decoded buried data.Furthermore, a preamble consisting of two sync words, an identificationword and a payload length word has to placed before the MPEG Audio frameand finally the IEC frame has to be padded with zeros. The transmitterreceives the CDDA PCM samples and generates subsequent frames eachhaving 1152 PCM samples. The available capacity for a buried datachannel is determined. Further the transmitter receives the MPEG audioframe and strips the first bits from said frame. The remaining bits ofsaid frame are randomized and a CRC word is determined for the remainingbits. To obtain the composite signal firstly, the header information isinserted in the LSB of the first PCM samples in a frame. Secondly, therandomized bits are inserted in the buried data channel payload. Finallythe CRC word is inserted in the last 16 bits of the buried data framepayload. The thus obtained composite signal is transmitted via atransmission medium.

The buried data channel is preferably used to transmit extra audiocontent within the 16-bit audio PCM data on a normal Audio CD. Thisextra audio content is preferably compressed according to the MPEG Audiostandard. As the first 16 bits of a MPEG Audio Frame are unique for theCD surround application they are not transmitted. In a CD surrounddecoding apparatus comprising an receiver which will be described below,these 16 bits are placed in front of the bits extracted from the burieddata channel stored in the PCM data.

FIG. 2 shows an embodiment of a receiver for receiving a compositesignal and generating a first and second digital information signaltherefrom. The composite signal comprises composite frames. A compositeframe has a second synchronization signal The receiver has an inputterminal 20 for receiving the composite signal. The composite signal issupplied to an detection unit 22 and unit 24. The detection unit 22 isarranged for detecting a second synchronization signal and generating adetection signal in response to a detected second synchronizationsignal. The detection signal is supplied to a control input of unit 24.Unit 24 is arranged for retrieving a composite frame from the compositesignal in response to the detection signal. The composite frames aresupplied to a first extraction unit 26 and a second extraction unit 28.The first extraction unit 26 is arranged for extracting at least a dataportion of a first frame of the first digital information signal from acomposite frame. The data portion of a first frame is supplied to signalcombination unit 32. The second extracting unit 28 is arranged forextracting at least a part of the second digital information signal froma composite frame so as to obtain a second frame of the second digitalinformation signal. The subsequent second frames, which form the seconddigital information signal, are supplied to output terminal 30.

The receiver further comprises a synchronization signal generator unit34. The synchronization signal generator unit 34 is arranged forgenerating a first synchronization signal. The first synchronizationsignal is supplied to the signal combination unit 32. The signalcombination unit 32 is arranged for combining the first synchronizationsignal and at least the data portion of a first frame so as to obtainthe first frame of the first digital information signal. The subsequentfirst frames are supplied to output terminal 36. The subsequent firstframes form the first digital information signal.

The receiver described above functions as follows. The composite signalis received at the input terminal 20. A transmitter as described abovegenerates the composite signal. The composite signal is a CDDA signalhaving left and right PCM samples. The CDDA signal comprises frames asdisclosed in FIG. 3. The CDDA signal comprises a buried data channel. Tobe able to retrieve the buried data from the CDDA signal each framecomprises header information. The header information comprises a secondsynchronization signal. The second synchronization signal is in thisembodiment in the two least significant bits of the first 6 L+R PCMsamples of each frame. However, other ways to insert the secondsynchronization signal are possible, for example in the leastsignificant bit of the first 12 L+R PCM samples. The synchronizationsignal detection unit 22 detects the second synchronization signal andgenerates a detection signal in response thereto. Unit 24 retrievesunder control of the detection signal the composite frames from the CDDAsignal. An embodiment of a frame is disclosed in FIG. 3. The secondextraction unit 28 receives the second frames to generate the seconddigital information signal. As in this embodiment a buried data channelis used there is no need to extract the unmodified bits of the originalsignal from the PCM samples of the second frame. In the event the nLSB's of each PCM sample are used to carry the first digital informationsignal, these bits will introduce audible noise. To reduce the audiblenoise the MSB's of the PCM samples have to be extracted from the secondframes.

The synchronization signal generator unit 34 generates a firstsynchronization signal. In the event the first digital informationsignal is an MPEG-2 Audio Layer II signal, the first 16 bits of eachframe are unique for the CD Surround application (0×FFFC, 12 bitsync+ID=mpeg-1+Layer-II+protection=used). Furtheremore a preambleconsisting of two sync words, an identification word. The firstsynchronization signal comprises at least this information. The firstextraction unit 26 extracts the header information from the secondframes. The header information comprises next to the sync signalinformation the bit allocation of the sub-frames. The bit allocationdefines the bits of the PCM samples belonging to the burried datachannel, thus the buried data frame payload. Next, unit 26 extracts theburied data from the second frames. Preferably, the buried data bits arerandomized written in the buried data channel. FIG. 4 shows anembodiment to de-randomize the buried data bits. The circuit comprisesan array of delays and exclusive OR's. The delays perform a one bitdelay function. The reference t_(n) represents inputted buried data bitn and S_(n) represents outputted de-randomized bit n. The circuitdisclosed in FIG. 4 performs the following operation:out=z[16]^z[14]^z[3]^z[1]^z[0], logical exclusive-or operator and z[n]is the bit extracted n bits back. At the start of a new frame the statez has to be initialized with all one's. The de-randomized data of aframe is supplied to combination unit 32. The first extraction unitpreferably comprises a CRC checking circuit. A diagram of said circuitis disclosed in FIG. 6. The last 16 bits of the buried data contain aCRC-16 word for error detection purposes. Each de-randomized buried databit, except for the last 16, is fed through a LFSR (Linear FeedbackShift Register) with polynomial 0×8005, as disclosed in FIG. 6. Thefinal state of the LFSR has to be compared with the buried data CRC-16word. If these two words are not the same, a transmission error hasoccurred.

Combination unit 32 receives the de-randomized data and calculates thepayload of the de-randomized data in a first from an MPEG-Audio frame ofthe first digital signal. The combination unit 32 combines the firstsynchronization signal generated by unit 34 and the calculated payloadso as to obtain the preamble of an MPEG Audio frame. The de-randomizeddata is place after the pre-amble. In the event the bit length of thepreamble and the de-randomized data is not in accordance to the lengthof a MPEG Audio frame, the frame has to be padded with zero's, so as toobtain the correct frame length. The thus obtained frames are suppliedto output terminal 36 to provide the first digital information signal atthe output of the receiver.

As described above, the first six PCM samples of a PCM frame contain thefirst 24 bits of a burried data frame, being a sync pattern. These 24bits preferably contain the code: 0×F87E1F(1111 1000 0111 1110 00011111).

It can be notes that the number of bits in a buried data frame be alwaysa multiple of eight, the de-randomization can be done very efficientlyper eight bits. Also the CRC-16 calculation can make use of this fact.Further, in the described format two bits are reserved in the buriedheader. These bits may be use for a possible future extension with aphysical channel and/or copy protection mode.

In accordance with the invention only one sync pattern is transmittedand the other sync and unique patterns of the MPEG Audio frames areregenerated in the receiver.

The extraction of the buried data payload contained in uniquelydecode-able buried data frames of 1152 stereo PCM samples performed byreceiver will be described now in more detail. A buried data frame issubdivided into three buried data subframes of 384 samples each. Eachsubframe for each channel has an individual allocation which is denotedby alloc[ch][sub frame]. For the corresponding channel “ch” and subframe“sub_frame”, this allocation indicates the number of LSB's of the PCMsample that is used to carry the buried data frame. The headerinformation is always contained in the LSB of the PCM samples. Theapplied frame structure is depicted in FIG. 1. In this example theallocation of the buried data subframes is as given in table 1.

TABLE 1 subframe allocation. alloc[ch][subframe] ch subframe 0 1 0 0 2 11 2 2 2 3

In order to extract the correct number of LSB's that are used to holdthe buried data payload, the header needs to be read and interpretedfirst. Dependent on the allocation information in the header, theremaining LSB's of the PCM samples that contain the header, may holdburied data payload.

For perceptual control of the header information and the buried datapayload, all the LSB's contained in buried_data_frame, except for thesyncword, have to pass bit by bit through a de-randomization circuitprior to interpretation. The de-randomization circuit is illustrated inFIG. 4. The following polynomial is appliedS _(n) =t _(n) ⊕t _(n-1) ⊕t _(n-3) ⊕t _(n-14) ⊕t _(n-16).

At the start of every frame all the states T_(i) are initialized to thebinary value 1.

FIG. 4 shows the de-randomization circuit. The blocks T represent shiftregisters. The additions represent “exclusive or gates”. At the start ofevery frame the shift registers are initialized to the binary value 1.For every new inserted input bit t_(n), a new output bit s_(n) isgenerated.

The bits have to be inserted into the de-randomization circuit in aspecific order which is explained in FIG. 5.

FIG. 5 showst The bits in the buried_data_frame need to be inserted intothe de-randomization circuit in a specific order. In the figure this isexplained by means of a simplified header and buried data payload.Assume that the syncword is only two 2 bits and the remaining header is6 bits. As illustrated in the figure, the allocation for the firstsubframe is 3 LSBs for the left channel and 2 bits for the rightchannel. The synchronization bits labeled “1” and “2” are read first anddo not pass through the randomization circuit. The remaining bits areread in the indicated order. This order is “header first” wherealternating the left and right channel is read. After that, the bits areread MSB first. All the bits labeled “3 . . . ” have to pass through therandomization circuit prior to interpretation.

The first action performed in a receiver is synchronization of thedecoder to the CD-DA PCM samples. The syncword is contained in the LSBof the PCM samples representing the left and the right channels. Thedistance between two consecutive syncwords amounts 2*1152 mono PCMsamples or 1152 stereo PCM samples. In order to retrieve the syncword, abit-stream is generated by successively concatenating the LSB of the PCMsample corresponding to the left channel and the LSB of the PCM samplecorresponding to the right channel. The last 16 bits of this bitstreamare continuously compared to the syncword. If there is a match for all16 bits, only then synchronization is achieved.

In another embodiment of a receiver two CRC checks are performed. Theerror detection methods used are “CRC-4” and “CRC-16” which generatorpolynomials areG(X)=X ⁴ +X ¹+1  (CRC-4)G(X)=X ¹⁶ +X ¹⁵ +X ²+1  (CRC-16)

The bits included in the CRC_(—)4 check are the bits after sync_word inthe header information. The bits included in the CRC_(—)16 check are thefirst bit after sync^(—)word in the header information to the positionof the crc16_check. The CRC method is depicted in the CRC-check diagramgiven in FIG. 6. For CRC-4, the initial state of the shift register is$F. For CRC-16, the initial state of the shift register is $FFFF. Allbits included in the CRC check are input to the circuit shown in theFIG. 6. After each bit is input, the shift register is shifted by onebit. After the last shift operation, the outputs bn . . . b0 constitutea word to be compared with the CRC-check word in the stream. If thewords are not identical, a transmission error has occurred in the fieldon which CRC-4 has been applied. To avoid annoying distortions,application of a concealment technique, such as muting of the actualframe or repetition of the previous frame is recommended. FIG. 6 shows aCRC-check diagram. The addition blocks represent “exclusive or” gates.

The following options of embedding the payload into the CD format areavailable. Firstly, by use of only the buried data channel. No use ismade of a physical channel. All header information for extracting theburied data payload, such as synchronization and allocation information,is merged with the buried data. The payload represents an MPEG-2 baseand extension frame.

Secondly, by making use of both a buried data channel and a physicalchannel. The header information is preferably contained in the physicalchannel. This information is merged with the payload in the physicalchannel. The payload in the physical channel represents an MPEG-2 baseframe. The buried data payload represents an MPEG-2 extension frame.

Thirdly, by making use of only a physical channel. The controlinformation is contained in the physical channel. This information ismerged with the payload in the physical channel. The payload representsan MPEG-2 base and extension frame.

In the case a physical limited multi level LML channel is present, italways contains the header. Dependent of whether a second channel isused, as signaled by the content_descriptor, the LML channel willcontain either the MPEG-2 base frame alone or additionally the MPEG-2extension frame. If a buried data channel is used, the start of thisframe will be synchronized with the extracted payload from the LMLchannel.

Also in the case where a physical channel is used, either in combinationwith a buried data channel or by itsself, the framing structure of theMPEG-2 payload remains based on frames of 1152 PCM stereo samples. Aframe of 1152 PCM audio samples corresponds to 192-F3 frames. AnF3-frame consists of 24 (user) bytes. During disc formatting, the startsof the frames of 1152 stereo PCM samples have been alligned with theF3-frames such that, after incorporation of the decoding delay of theLML data as a result of error correction, the data from the two channelsis of the same frame. This is illustrated in FIG. 7.

FIG. 7 shows a frame of 1152 stereo PCM samples corresponds to 192 F3frames. At the moment the synchronization pulse is detected at the“synchronization point”, data at the “frame start point” becomesavailable from the physical channel. For that specific frame, PCM datastarts reading at the “synchronization point”.

At any synchronization point, at least 111 F3-frames need to beavailable in the buffer in order to have the proper amount of physicaldata available from that point onwards. If this is not the case,decoding can only start at the next synchronization point.

The actual extraction of the physical payload is independent of theprocessing related to the buried data channel. For each frame of 1152CD-DA PCM samples, A fixed amount of 290 kbytes of physical payloadbecomes available. The physical data becomes available byte for byte andis interpreted MSB first. After the header information is read, the datarepresenting the MPEG encrypted MPEG-2 base (+extension) frame is read.

In the case the control information is not contained in the buried datachannel, the extraction of the payload can start at the first PCM sampleof the left channel. Synchronization and header information is containedin the physical channel. The “alloc” information describes the amount ofembedded bits per buried data sub frame. An example is given in FIG. 8.Apart from the payload data, room is reserved for a CRC-16 that operateson the full payload contained in the buried data channel. In the casethe buried data payload is zero, no CRC-16 is written.

The buried data payload and additionally, if present, the physicalpayload within one frame of 1152 CD-DA PCM samples represent oneencrypted MPEG-2 audio bitstream that contains 1152 multi-channel audioPCM samples. In the case no physical channel is used, the buried datapayload represents a complete encrypted MPEG2 audio stream (base plusextension). In the case a physical channel is used, the buried datapayload represents an MPEG-2 extension stream and the physical payloadrepresents the encrypted MPEG-2 base frame stream. The number of bitscontained in an encrypted MPEG2 base frame may not exceed the capacityavailable in the LML channel. The number of bits contained in theencrypted MPEG2 extension frame is variable and is a multiple of 8 bits.The division described above is illustrated in FIG. 9.

In the case a physical channel is used, the encrypted MPEG-2 base framebits for the corresponding frame are extracted and put in front ofburied_data_bits. It should be noted that a record carrier with aphysical channel is known from U.S. Pat. No. 5,210,738 and U.S. Pat. No.5,724,327 (PHN 13.992)

The complete bit-stream (base+extension) is decrypted and subsequentlyMPEG2 decoded, resulting in 1152 multi-channel PCM audio samples.

For the decoding of MPEG2 audio data reference is made to ISO/IEC13818-3.

FIG. 10 illustrates transmitter 40 which may include detector 42 fordetecting the capacity available in a second frame to insert a firstframe and generating a control signal for controlling the datacompression of the third digital information signal, the control signalbeing indicative for the capacity available in the second frame.Transmitter 40 may also include channel-encoder 44 for channel encodingthe transmission signal prior to transmitting the transmission.

Whilst the invention is described with reference to preferredembodiments thereof, it is to be understood that these are notlimitative examples. Thus various modifications may become apparent tothose skilled in the art, without departing from the scope of theinvention, as defined by the claims.

The word ‘comprising’ does not exclude the presence of other elements orsteps than those listed in a claim. Any reference signs do not limit thescope of the claims. The invention can be implemented by means of bothhardware and software. Several means may be represented by the same itemof hardware. Further the invention lies in each and every novel featureor combination of features.

1. Transmitter for transmitting a first and second digital information signal via a transmission medium, said first digital information signal comprising first frames having at least a first synchronization signal and a data portion stored in them, the transmitter comprising: input means for receiving the first and second digital information signal; processing means for processing the second digital information signal into subsequent second frames, said second frames comprising blocks of information of the second digital information signal; signal combination means for inserting a second synchronization signal and at least the data portion of a first frame into a second frame of the second digital information signal so as to obtain a composite frame; output means for supplying the composite frames to an output terminal so as to obtain a composite signal to be transmitted; characterized in that said signal combination means are adapted to strip the first synchronization signal from said first frames prior to inserting at lease the data portion of the first frames into the second frames.
 2. Transmitter as claimed in claim 1, characterized in that the signal combination means are adapted to insert the data portion of a first frame into a second frame of the second digital information signal by using buried data techniques.
 3. Transmitter as claimed in claim 1, characterized in that a second frame represents a portion of the second digital information signal of a predefined duration and a first frame represents a portion of a third digital information signal of a substantially the same duration.
 4. Transmitter as claimed in claim 3, characterized in that the first digital information signal is obtained by data compression of the third digital information signal.
 5. Transmitter as claimed in claim 4, characterized in that the first digital information signal is in the form of an MPEG encoded signal.
 6. Transmitter as claimed in claim 4, characterized in that the transmitter further comprises means for detecting the capacity available in a second frame to insert a first frame and generating a control signal for controlling the data compression of the third digital information signal, said control signal being indicative for the capacity available in said second frame.
 7. Transmitter as claimed in claim 1, characterized in that the second digital information signal comprises at least one PCM signal.
 8. Transmitter as claimed in claim 1, the transmitter being in the form of an apparatus for recording the digital information signal on a record carrier.
 9. Transmitter as claimed in claim 1, characterized in that the transmitter further comprises channel-encoding means for channel encoding the transmission signal prior to transmission.
 10. Transmitter as claimed in claim 1, wherein: the signal combination mean are adapted to insert the data portion of a first frame into a second frame of the second digital information signal by using buried data techniques; a second frame represents a portion of the second digital information signal of a predefined duration and a first frame represents a portion of a third digital information signal of a substantially the same duration; the first digital information signal is obtained by data compression of the third digital information signal; the first digital information signal is in the form of an MPEG encoded signal; the transmitter further comprises means for detecting the capacity available in a second frame to insert a first frame and generating a control signal for controlling the data compression of the third digital information signal, said control signal being indicative for the capacity available in said second frame; the second digital information signal comprises at least one PCM signal; the transmitter being in the form of an apparatus for recording the digital information signal on a record carrier; and the transmitter further comprises channel-encoding means for channel encoding the transmission signal prior to transmission.
 11. Method of transmitting a first and second digital information signal via a transmission medium, said first digital information signal comprising first frames having at least a first synchronization signal and a data portion stored in them, the method comprising the steps: receiving the first and second digital intonation signal; processing the second digital information signal into subsequent second frames, said second frames comprising blocks of information of the second digital information signal; inserting a second synchronization signal and at least the data portion of a first frame into a second frame of the second digital information signal so as to obtain a composite frame; supplying the composite frames to an output terminal so as to obtain a composite signal to be transmitted; characterized in that method further comprises the step stripping the first synchronization signal from said first frames prior to inserting at least the data portion of said first frames into the second frames.
 12. Method as claimed in claim 11, characterized in that the at least the data portion of a first frame is inserted into a second frame at the second digital information signal by using buried data techniques.
 13. Method as claimed in claim 11, characterized in that a second frame represents a portion of the second digital information signal of a predefined duration and a first frame represents a portion of a third digital information signal of a substantially the sane duration.
 14. Method as claimed in claim 13, characterized in that the first digital information signal is obtained by data_compression of the third digital information signal.
 15. Method as claimed in claim 14, characterized in that the first digital information signal is in the form of an MPEG encoded signal.
 16. Method as claimed in claim 11, wherein: the at least the data portion of a first frame is inserted into a second frame of the second digital information signal by using buried data techniques; a second frame represents a portion of the second digital information signal of a predefined duration and a first frame represents a portion of a third digital information signal of a substantially the sante duration; the first digital information signal is obtained by data compression of the third digital information signal; and the first digital information signal is in the form of an MPEG encoded signal.
 17. Transmission medium in the form of a record carrier carrying a composite signal comprising portions of a first and a second digital information signal, said composite signal being a sequence of composite frames, a composite frame comprises a second synchronization signal and a data portion of a first frame of the first digital information signal, said first frame comprises a first synchronization signal and a data portion, said composite frame being obtained by inserting the second synchronization signal and at least the data portion of the first digital information signal into a second frame of the second digital information signal, a second frame being obtained by processing the second digital information signal into subsequent second frames, said second frames comprising blocks of information of the second digital information signal, characterized in that prior to inserting at least the data portion of a first frame the first synchronization signal is stripped from said first frame.
 18. Transmission medium as claimed in claim 17, characterized in that at least the data portion of a first frame is inserted in a second frame by using buried data techniques.
 19. Transmission medium as claimed in claim 17, characterized in that a second frame represents a portion of the second digital information signal of a predefined duration and a first frame represents a portion of a third digital information signal of substantially the same duration.
 20. Transmission medium as claimed in claim 19, characterized in that the first digital information signal is obtained by data compression of the third digital information signal.
 21. Transmission medium as claimed in claim 17, wherein the record carrier is of the optical or magnetical recording type.
 22. The transmission medium of claim 17, wherein: at least the data portion of a first frame is inserted in a second frame by using buried data techniques; a second frame represents a portion of the second digital information signal of a predefined duration and a first frame represents a portion of a third digital information signal of substantially the same duration; the first digital information signal is obtained by data compression of the third digital information signal; and the record carrier is of the optical or magnetical recording type. 